Three-dimensional printers fabricate parts by applying material in layers onto a build surface; the build surface provides a substrate onto which the material is sequentially applied to gradually form the desired structure of the part. In one class of printers, molten material is applied in layers and solidifies as it cools.
In a typical example, a print head that applies the molten material is mounted to move along X and Y axes in a horizontal plane, and the build platform is mounted to a horizontal support that is vertically movable along the Z axis relative to the plane in which the print head moves. In other printers, the movements along the axes may differ such that the horizontal support may provide the X- or Y-axis motion relative to the print head. In all cases, to fabricate a part, the horizontal support is moved relative to the print head to place the build platform very close to the movement plane of the print head, which then moves within the horizontal plane to apply an initial layer of material onto the platform. Once the initial layer is applied to the platform surface, the horizontal support is sequentially moved away from the movement plane of the print head to apply subsequent layers to build up the part.
For accuracy, the build surface should be parallel to the plane in which the print head moves. Some discrepancy in such parallelism can be overcome by applying an initial layer of material that varies in thickness to provide a surface that is planar relative to the plane of the print head; however, this approach is wasteful of both time and material. To align the platform with the plane of the print head, printers typically employ an array of set screws that extend between the platform (or a subframe to which a removable platform is attached by clips) and the horizontal support to allow fine adjustment of the orientation of the platform relative to the horizontal support. Compression springs that encircle the set screws serve to tension the platform and, to some degree, serve to maintain the position of the screws once adjusted. In practice, the screws frequently loosen in use, requiring frequent readjustment. Additionally, since only a small number of screws are employed to level the platform (or subframe), and the adjustment procedure is tedious as adjusting one screw alters the level of the entire platform relative to the other screws, requiring them to be further adjusted in an iterative procedure.
An additional problem results when the build surface is not sufficiently planar. In such cases, the initial layer of material may have an uneven layer thickness that can cause the incomplete part to peel from the build surface due to uneven thermal contraction as additional layers of material are applied and then cool.
The platform assembly of the present invention overcomes the above limitations while remaining simple and economical, so as to provide significantly improved performance for 3D printers suitable for consumer use.